Despite the high diversity of forests found in the Neotropics, Neotropics there is an insufficient knowledge of the characteristics and role of the ECM symbiosis in these ecosystems. This chapter summarizes and describes the range of Angiospermae and Gymnospermae forests forests growing in South America South America in which ECM studies have been carried. Most studies on mycorrhizal status have been carried for the Fagaceae, Fabaceae, Nyctaginaceae, and Polygonaceae families, while most ECM inoculums types have been applied to introduce species. The associated fungi recorded in the ECM anatomotypes reviewed were mostly Basidiomycota with most anatomotypes described for native species. This knowledge is essential for the better understanding of the plant–fungus mutualism in ECM associations in South America.